test: simplify redundant code

Remove the function 'test_unop', as the cases therein are redundant to
those handled by 'unary_operator'; exception: the cases 'o' and 'N':
they had been present in test_unop and handling the commands
  test -N STR
  test -o STR
and
  test x = x -a -N STR
  test x = x -a -o STR
which ran into an error later on anyway.
With this commit, the error diagnostic will change from ...
  $ /usr/bin/test -N STR
  /usr/bin/test: extra argument '-N'
  $ /usr/bin/test -o STR
  /usr/bin/test: extra argument '-o'
... to ...
  $ src/test -N STR
  src/test: '-N': unary operator expected
  $ src/test -o STR
  src/test: '-o': unary operator expected

* src/test.c (test_unop): Remove.
(unary_operator): Fail with test_syntax_error in the default case.
(term): Directly call unary_operator.
(two_arguments): Likewise.
* tests/misc/test-diag.pl: Adjust error diagnostic.

1 files changed, 2 insertions, 2 deletions

diff --git a/tests/misc/test-diag.pl b/tests/misc/test-diag.pl
index 91356ef56..f543f9f09 100755
--- a/tests/misc/test-diag.pl
+++ b/tests/misc/test-diag.pl
@@ -26,8 +26,8 @@ use strict;
 my @Tests =
     (
      # In coreutils-5.93, this diagnostic lacked the newline.
-     ['o', '-o arg', {ERR => "test: extra argument '-o'\n"},
-      {ERR_SUBST => 's!^.*:!test:!'},
+     ['o', '-o arg', {ERR => "test: '-o': unary operator expected\n"},
+      {ERR_SUBST => 's!^.*test:!test:!'},
       {EXIT => 2}],
     );